Assessing of The Strength of Concrete of Qazvin's Irrigation Canal Using Twist-off method

Use of channels cover to increase strength of their soil walls against permeability decrease and other water losses for increase of water transmitting efficiency is avital issue. As covers are expensive, choosing of them should be done with great accuracy. One of these covers is concrete cover. So, some studies have been made for assessing of quality of this type of cover. In this study, in-situ strength of concrete cover of channels in Qazvin has been evaluated using twist-off method. This method is a partial-destructive method and it is so fast, low cost, accurate, simple and applicable for all kinds of horizontal and vertical concrete surfaces. Our research showed that the covers are 40-year old with in-situ strength of 14-34 MPa. Concrete cover under water level are exposed to wetting and drying, frequent freezing and thawing and permanent corrosion. So, this part of cover under sulphate and cloridric attacks more. Because of that, in-situ strength of this part smaller that the concrete higher that the under level. After twist_ off test, the concrete covers that have insufficient strength should be replaced. Also, the new concrete cover should resistant against physical and chemical damages. So, it is needed to cement content, w/c ratio, aggregate size and pozzolan content, executive condition and curing be considered. Then efficiency of water transmitting will increase.